微波能量传输系统设计及试验

面向空间太阳能电站应用,进行了固态体制微波能量传输技术研究。针对能量传输波束扩散导致收集效率低的问题,研究了基于人工媒质理论设计的完美匹配层的能量接收整流表面,通过调节人工媒质单元的结构参数实现天线输出阻抗与整流电路输入阻抗的共轭匹配,同时抑制整流电路高次谐波,省去原有匹配及低通滤波器,简化电路结构、实现高效微波能量吸收与转换。以空间太阳能电站规定的波束中心传输微波功率密度限制作为能量接收整流表面设计的约束条件,设计能量接收整流表面,结合固态体制微波能量发射端,搭建5.8GHz小规模微波能量传输系统开展了地面试验验证,实测结果显示整流表面能量转换效率最高为57.7%。此次试验验证了先进的固态能量传输试验系统,为空间太阳能地面缩比试验及未来空间太阳能电站的建设提供了技术支撑。     

Yarkovsky-Schach effect on space debris motion

The Yarkovsky-Schach effect is a small perturbation affecting Earth satellites and space debris illuminated by the Sun. It was first applied to the orbit of LAGEOS satellites as an explanation of the residuals in orbital elements. In this work, we carry out several numerical integration tests taking into consideration various orbit and rotation parameters, in order to analyse this effect in a broader context. The semi-major axis variations remain small and depend on the spin axis attitude with respect to the Sun. We show that the force amplitude is maximised for orbits inclined with $i\approx$?20–30°. We also observe the influence on other orbital elements, notably on the orbit inclination. However, these effects are clearly observed only on long timescales; in our simulations, we propagated the orbits for 200?y. The Yarkovsky-Schach effect is thus confirmed to have a minuscule magnitude. It should be taken into account in studies requiring high-precision orbit determination, or on expanded timescales.     

Optimal Earth’s reentry disposal of the Galileo constellation

Nowadays there is international consensus that space activities must be managed to minimize debris generation and risk. The paper presents a method for the end-of-life (EoL) disposal of spacecraft in Medium Earth Orbit (MEO). The problem is formulated as a multiobjective optimisation one, which is solved with an evolutionary algorithm. An impulsive manoeuvre is optimised to reenter the spacecraft in Earth’s atmosphere within 100?years. Pareto optimal solutions are obtained using the manoeuvre $\mathrm{\Delta }v$ and the time-to-reentry as objective functions to be minimised. To explore at the best the search space a semi-analytical orbit propagator, which can propagate an orbit for 100?years in few seconds, is adopted. An in-depth analysis of the results is carried out to understand the conditions leading to a fast reentry with minimum propellant. For this aim a new way of representing the disposal solutions is introduced. With a single 2D plot we are able to fully describe the time evolution of all the relevant orbital parameters as well as identify the conditions that enables the eccentricity build-up. The EoL disposal of the Galileo constellation is used as test case.     

Simulation-based evaluation of a cold atom interferometry gradiometer concept for gravity field recovery

The prospects of future satellite gravimetry missions to sustain a continuous and improved observation of the gravitational field have stimulated studies of new concepts of space inertial sensors with potentially improved precision and stability. This is in particular the case for cold-atom interferometry (CAI) gradiometry which is the object of this paper. The performance of a specific CAI gradiometer design is studied here in terms of quality of the recovered gravity field through a closed-loop numerical simulation of the measurement and processing workflow. First we show that mapping the time-variable field on a monthly basis would require a noise level below $5\text{mE}/\sqrt{\text{Hz}}$. The mission scenarios are therefore focused on the static field, like GOCE. Second, the stringent requirement on the angular velocity of a one-arm gradiometer, which must not exceed ${10}^{-6}$?rad/s, leads to two possible modes of operation of the CAI gradiometer: the nadir and the quasi-inertial mode. In the nadir mode, which corresponds to the usual Earth-pointing satellite attitude, only the gradient $V_{\mathit{yy}}$, along the cross-track direction, is measured. In the quasi-inertial mode, the satellite attitude is approximately constant in the inertial reference frame and the 3 diagonal gradients $V_{\mathit{xx}}\text{,}{V}_{\mathit{yy}}$ and $V_{\mathit{zz}}$ are measured. Both modes are successively simulated for a 239?km altitude orbit and the error on the recovered gravity models eventually compared to GOCE solutions. We conclude that for the specific CAI gradiometer design assumed in this paper, only the quasi-inertial mode scenario would be able to significantly outperform GOCE results at the cost of technically challenging requirements on the orbit and attitude control.     

An estimation of Envisat’s rotational state accounting for the precession of its rotational axis caused by gravity-gradient torque

The rotational state of Envisat is re-estimated using the specular glint times in optical observation data obtained from 2013 to 2015. The model is simplified to a uniaxial symmetric model with the first order variation of its angular momentum subject to a gravity-gradient torque causing precession around the normal of the orbital plane. The sense of Envisat’s rotation can be derived from observational data, and is found to be opposite to the sense of its orbital motion. The rotational period is estimated to be $(120.674\pm 0.068)·\exp \left((4.5095\pm 0.0096)\times {10}^{-4}·t\right)\text{s}$, where t is measured in days from the beginning of 2013. The standard deviation is 0.760?s, making this the best fit obtained for Envisat in the literature to date. The results demonstrate that the angle between the angular momentum vector and the negative normal of the orbital plane librates around a mean value of $8.53°\pm 0.42°$ with an amplitude from about $0.7°$ (in 2013) to $0.5°$ (in 2015), with the libration period equal to the precession period of the angular momentum, from about 4.8?days (in 2013) to 3.4?days (in 2015). The ratio of the minimum to maximum principal moments of inertia is estimated to be $0.0818\pm 0.0011$, and the initial longitude of the angular momentum in the orbital coordinate system is $40.5°\pm 9.3°$. The direction of the rotation axis derived from our results at September 23, 2013, UTC 20:57 is similar to the results obtained from satellite laser ranging data but about $20°$ closer to the negative normal of the orbital plane.     

Libration and end body swing stabilization of a parallel partial space elevator system

This paper studies the libration and stabilization of a parallel partial space elevator system in circular orbits. The system is made up of two paralleled partial space elevators, each of which consists of one main satellite, one end body and a climber moving along the tether between them. The libration characteristics of the elevator are studied through numerical analysis by a new dynamic model, and a novel control strategy is proposed to stabilize the swing of the end body by projecting the climber speeds only. Optimal control method is used to implement the new control strategy in the case where the climbers move in opposite direction. The simulation results validate the effectiveness of the proposed control strategy whose application will neither sacrifice the transport efficiency nor exacerbate libration significantly.     

MIMO空间通信格约简TH预编码分析与改进

为了评价现有MIMO空间通信预编码方案并改进, 分析与仿真了基于迫零和最小均方误差准则的联合LLL格约简非线性TH预编码算法. 在TH预编码基础上, 通过改善信道矩阵奇异性, 提出了改进的格约简TH预编码方法. 仿真表明, 采用最小均方准则的预编码MIMO系统性能优于采用迫零准则的系统; 所提格约简TH预编码算法相对现有的TH编码算法, 在采用LLL格约简而使复杂度下降时, 仍可获得相对较好的误码性能, 适合多天线MIMO空间传输预编码等 应用.      

空间绳系机器人抓捕非合作目标的质量特性参数辨识

针对空间绳系机器人抓捕非合作目标/空间垃圾后需要对其进行回收/拖曳的精确控制问题,提出了一种利用抓捕后保持阶段的振动特性辨识目标参数的方法。首先,根据质量特性参数辨识的需要,推导了系统的动力学模型。不同于以往将本体卫星和被抓捕目标简化为质点的动力学模型,本文针对任意的目标抓捕位置,在考虑重力梯度影响的基础上,利用拉格朗日法获得系统各广义坐标的动力学公式。然后,分析非合作目标和系绳在后抓捕保持阶段的姿态运动。最后,在非合作目标与本体卫星没有任何信息交互的情况下,利用后抓捕阶段目标卫星和系绳特有的振动,并使用具有鲁棒性可遗忘因子的递推最小二乘法,提出了包括转动惯量和质心到任意抓捕点距离在内的质量特性参数辨识算法。     

某空间伸杆机构的摩擦补偿及反步自适应控制

面向某新型大伸展(收拢比)、高载荷(自重比)伸缩式空间伸杆机构的实际应用需求,研究其低速伸展过程中摩擦力矩补偿及其反步自适应控制方法。考虑伸杆伸长量等各种因素引起的摩擦力矩变化,将其等效描述为摩擦变化系数的影响,由此得到LuGre改进模型的摩擦表征。在此基础上,设计基于摩擦力矩补偿的反步自适应控制器,以补偿和抑制模型不确定性和摩擦影响。最后通过仿真校验表明,该方法不依赖精确的动力学模型,能够在保证鲁棒性的前提下有效提高系统控制性能。     

空间绳系机器人单目视觉伺服控制系统

为解决空间绳系机器人近距离交会对接中的目标测量问题,设计了一种单目视觉伺服控制系统。该系统针对小模板在大场景中匹配时存在鲁棒性差、耗时长等缺点,采用了一种新的模板匹配算法。匹配模板借鉴FAST算法的空心圆环结构,使得算法具有旋转不变性,也减小了因背景变化引起的累积误差。同时匹配准则采用灰度值+梯度值的复合算子,具有较强的抗噪声和抑制光照变化的能力。为避免因错误匹配和遮挡等引起的跟踪失败,还设计了动态模板更新策略;最后结合最小二乘综合位置预测方法和PD控制器,实现了对复杂场景中的非合作目标的实时跟踪逼近。